Integration of fibers on substrates fabricated with grooves

ABSTRACT

Techniques and devices for integrating optical fibers on substrates with grooves for various optical applications. Two openings that penetrate through the substrate are formed at both ends of each groove to allow a fiber to pass from one side of substrate to another side. The fiber cladding of a fiber portion positioned in the groove can be removed to produce an optical coupling port.

This application claims the benefit of U.S. Provisional Application Nos.60/214,686 entitled “Wafer scale fiber optic device fabricationtechnique for mass production”, and 60/214,589 entitled “An integratablefiber optic coupling technique,” both of which were filed on Jun. 27,2000.

TECHNICAL FIELD

This application relates to integration of optical fibers on substratesto form various optical devices, and more specifically, to techniquesand designs for integrating optical fibers in grooves formed insubstrates.

BACKGROUND

Optical fibers are widely used in transmission and delivery of opticalsignals from one location to another in a variety of optical systems,including but not limited to fiber links and fiber networks for datacommunications and telecommunications. A typical fiber may be simplifiedas a fiber core and a cladding layer surrounding the fiber core. Therefractive index of the fiber core is higher than that of the fibercladding to confine the light. Light rays that are coupled into thefiber core within a maximum angle with respect to the axis of the fibercore are totally reflected at the interface of the fiber core and thecladding. This total internal reflection provides a mechanism tospatially confine the optical energy of the light rays in one or moreselected fiber modes to guide the optical energy along the fiber core.

The guided optical energy in the fiber, however, is not completelyconfined within the fiber core. A portion of the optical energy “leaks”through the interface between the fiber core and the cladding via anevanescent field that essentially decays as an exponential function ofthe distance from the core-cladding interface. The distance for a decayin the electric field of the guided light by a factor of e≈2.718 isabout one wavelength of the guided optical energy. This evanescentleakage may be used to couple optical energy into or out of the fibercore, or alternatively, to perturb the guided optical energy in thefiber core.

For example, when two fiber cores are closely spaced from each other bya spacing on the order of one wavelength or less, optical couplingoccurs between the two fiber cores through the overlap of the evanescentfields of the two fiber cores. This structure can be used to constructoptical fiber couplers.

SUMMARY

One embodiment of the fiber devices of the present disclosure includes asubstrate that is formed with an elongated groove on one substratesurface, and two openings respectively at two ends of the groove formedthrough the substrate to extend between the two sides of the substrate.An optical fiber is engaged to the substrate by passing through the twoopenings. The fiber has at least first, second, and third contiguousfiber portions, where the second fiber portion is disposed in theelongated groove on one side of the substrate, and the first and thirdfiber portions are located on or over the opposite substrate surface.The fiber cladding in the second fiber portion may be at least partiallyremoved to form an optical coupling port for the fiber.

According to another embodiment, a fiber device may be formed in asubstrate that includes grooves formed on both opposing sides of thesubstrate. The substrate has first and second opposing substratesurfaces, and first, second, and third openings that are spaced along astraight line and go through the substrate to extend between the firstand the second substrate surfaces.

The first groove, elongated along the straight line and formed over thefirst substrate surface between the first and second openings, isconfigured to have a first end connected to the first opening and asecond end connected to the second opening. The second groove, elongatedalong the straight line and formed over the second substrate surfacebetween the second and third openings, is configured to have a first endconnected to the second opening and a second end connected to the thirdopening. An optical fiber is engaged to the substrate by passing throughthe first, second, and third openings in the substrate to have a firstfiber portion positioned in the first groove and a second fiber portionpositioned in the second groove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of a fiber device that integrates a fiber toa substrate with a groove for positioning the fiber and openings forholding the fiber.

FIGS. 2A and 2B show a cross sectional view of the device in FIG. 1along the direction AA′ and a side view of the device in FIG. 1 alongthe direction BB′, respectively.

FIGS. 3A and 3B show examples of two different cross sections forgrooves shown in FIG. 1.

FIGS. 4A, 4B, 5A, 5B, 5C, 5D, and 5E illustrate a process of fabricatingV grooves in semiconductor substrates by anistropic etching.

FIG. 6 illustrates formation of openings in V grooves by anistropicetching.

FIG. 7A shows a substrate that is fabricated with an array of grooveswith openings.

FIG. 7B shows a fiber device formed on a substrate with two or moregrooves aligned with each other along a straight line on a single sideof the substrate.

FIGS. 7C and 7D show fiber devices formed on a substrate with grooves ona single side of substrate that are oriented in different relativedirections.

FIGS. 8A, 8B, 8C, 8D, and 9 illustrate substrates that are processedwith grooves on both substrate surfaces.

FIG. 10 shows a substrate processed with grooves on both substratesurfaces, where openings at both ends of each groove are separatelyfabricated from the V grooves.

FIGS. 11 and 12 show exemplary fiber devices by integrating fibers tosubstrates with grooves.

FIG. 13A shows uses of relative positions between grooves to controloptical coupling between fibers positioned in the grooves.

FIG. 13B shows a substrate with both deep and shallow grooves formed ona single side.

FIG. 13C shows a substrate with both deep and shallow grooves formed onboth sides.

FIG. 14 shows an exemplary fiber device that has lateral jump-channelgrooves on the substrate to change a direction of a fiber in thesubstrate plane.

DETAILED DESCRIPTION

FIGS. 1, 2A, and 2B illustrate one embodiment of a fiber device 100 thatintegrates a fiber 140 to a substrate 110. The device 100 may be used asa building block to construct a variety of fiber devices, including butnot limited to, fiber couplers, fiber attenuators, fiber modulators,fiber beam splitters, optical fiber switches, and fiberfrequency-division multiplexers.

The substrate 110 may be formed of various materials, such assemiconductors, insulators including dielectric materials (e.g., aglass, a quartz, a crystal, etc), metallic materials, or any othersolid-state materials that can be processed to form the device featuressuch as grooves and through holes disclosed herein. Two parallel andopposing substrate surfaces, 112 and 114, are generally flat and may bepolished. An elongated groove 120 is formed in the substrate 110 on thesurface 112 and is essentially a recess from the surface 112. The groove120 may be fabricated by removing a portion of the material from thesubstrate 110 through etching or other processes.

The geometry of the groove 120 is generally elongated along a straightline as illustrated or along a curved line. Unless otherwise indicated,the following description will use straight-line grooves as examples.Some embodiments are described with specific reference to groove withV-shaped cross sections as shown by the groove 310 in FIG. 3B. The crosssections are generally not so limited and may also be other shapes aswell, including rectangular as shown in FIG. 2A, U-shaped as shown bythe groove 310 in FIG. 3A, a circularly shape or other suitable shapes.

The width, W, of the groove 120 is generally greater than the diameter,d, of the fiber 140 and may either remain a constant or vary spatiallyalong the groove 120, e.g., increasing from the center towards the twoends. The length, L, of the groove 120 may vary from one grove toanother and can be determined based on specific requirements ofapplications. The depth D of the groove 120 may be a constant or mayvary along the groove 120, e.g., increasing from the center towards thetwo ends. In general, at least a portion of the groove 120 has a depth Dless than the fiber diameter d but greater than the sum of the fiberradius r=d/2 and radius of the fiber core r_(c)=d_(c/)2. This portion ofthe groove 120 exposes partial fiber cladding of the fiber 140 above thesurface 112 while still keeping the fiber core below the surface 112.Other portions of the groove 120 may have a depth that is at least thefiber diameter d so that the fiber can be essentially placed in thegroove 120 below the surface 112. However, in certain applications suchas the device shown in FIG. 12, the depth D of the entire groove 120 maybe greater than fiber diameter d. Unless otherwise indicated, thefollowing description will assume that at least a portion of the groove120 has a depth D that satisfies (d+d_(c))/2<D<d. For example, thecentral portion of the groove 120 may have a depth D less than d whilethe portions on either sides of the central portion may have a depthequal to or greater than the fiber diameter d.

Notably, the fiber device 100 includes two openings 131 and 132 that arerespectively formed at the two ends of the groove 120 and penetratethrough the substrate 110. Hence, the openings 131 and 132 are throughholes extending between the two surfaces 112 and provide access from onesurface (112 or 114) to another. The spacing between the openings 131and 132 essentially determines the length L of the groove 120. Theaperture of the openings 131 and 132 should be sufficiently large toreceive the fiber 140, e.g., with a diameter greater than the diameterof the fiber 140. The shape of the holes 131 and 132 may generally be inany suitable geometry.

A portion of the fiber 140 is placed in the groove 120 near the surface112. The remaining portions 141, 142 of the fiber 140 on both sides ofthe portion in the groove 120 are respectively fed through the first andsecond openings 131, 132 to the other side 114 of the substrate 110.After being placed in the substrate 110 as shown in FIG. 1, the fiber140 may be slightly pulled by moving the fiber portions 141 and 142 inopposite directions so that the portion of the fiber 140 in the groove120 is in substantially full contact with the groove 120.

Since a portion of the groove 120 has a depth D less than the fiberdiameter d, the cladding of the fiber 140 in this portion protrudes outof the surface 112. The fiber core in this portion of the fiber isgenerally kept under the surface 112. For example, the cladding of acentral portion of the fiber 140 between the holes 131 and 132 may beexposed. This protruded or exposed cladding is then removed and polishedto form a flat surface 144 of a length Lc that is above the fiber core143 and is substantially coplanar with the surface 112 of the substrate110. When the spacing, h, between the flat surface 144 and the fibercore 142 is sufficiently small (e.g., on the order of one wavelength orless), the flat surface 144 can be used to couple optical energy into orout of the fiber core 144 through the evanescent fields outside thefiber core. Hence, the length, Lc, of the flat surface 144 approximatelyrepresents the optical coupling length for the fiber device 100.

FIGS. 4A and 4B illustrate the fabrication of the V groove 320 andplacement of the fiber 140 in the V groove 320 as shown in FIG. 3B.First, a mask layer 410 is deposited over the surface 112 of thesubstrate 110 and is patterned by a suitable technique such as aphotolithography process to have one or more groove areas exposing theunderlying substrate 110. Next, the exposed portions of the substrate110 are anistropically etched to form V grooves.

If the substrate 110 is formed of a semiconductor, e.g., silicon, athermally-grown silicon oxide or nitride film may be used as the etchingmask 410 for anisotropic silicon etching. When the surface 112 is in thecrystalline plane (100) of the Si substrate 110 and the groove patternsin the etching mask 410 are parallel to the crystalline plane (110), anetchant chemical such as alkaline (KOH) can be applied on the silicon(100) surface to produce truncated v-shaped grooves. Since theanisotropic etching is stopped at the crystalline plane (111), thedimension of the V grooves, such as the groove width and depth can beaccurately controlled by properly selecting the dimension of the groovepatterns formed in the etching mask 410.

Referring to FIG. 4B, after the grooves 320 are formed, the fibers 140can be placed in the grooves 320 and bonded to the groves 320 atlocations 420. The bonding may be implemented by a number of techniques,including but not limited to using an epoxy, glass frit thermal bond, orCO2 assisted thermal bond. When multiple grooves 320 are formed, anarray of fibers 140 can be precisely aligned in the grooves 320 with apredetermined spacing. The exposed cladding of the fiber 140 can then beremoved and polished to form the flat surface 144 as shown in FIG. 3B.

FIG. 5A shows one exemplary groove pattern 500 formed in the etchingmask layer 430 in FIG. 4A. FIG. 5B illustrates the corresponding Vgroove 320 in the silicon substrate 110 formed from the anistropicetching by using the mask 500. The opening of the groove pattern 500 isdesigned to gradually widen from the center to both sides along thegroove to be formed. Accordingly, the width and depth of the underlyingV groove 320 also increase from the center portion 510 to side portions520 that are spaced from the center along the groove 320. Asillustrated, the surfaces of the V groove 320 are not flat but arecurved as a result of etching through the above mask 500. FIGS. 5C, 5D,and 5E show the placement of fibers 140 in the above V-groove structure.

The above anistropic etching may be used to form both the V groove 320and the openings 131 and 132 at both sides of the V groove 320 as shownin FIG. 1. Referring to FIG. 6, when opening of the groove pattern 500in the etching mask 410 is sufficiently wide, side portions 620 of the Vgroove 610 can extend all the way through the substrate 110 from thesurface 112 to the opposite surface 114 and hence create an opening 620on the surface 114. The openings 620, therefore, can be used as theopenings 131 and 132 to allow the fiber 140 to go through the substrate110 from the surface 112 to the opposite surface 114.

FIGS. 7A and 7B show that an array 700 of such V grooves 710 with twoopenings can be formed on one side of the substrate 110. The V grooves710 may be aligned to be parallel to one another along their elongateddirections and are arranged to form multiple parallel columns 730 with aspacing 740. Within each column 730, multiple V grooves 710 may bespaced from one another by a spacing 720. The substrate 110 with thearray 700 may diced into multiple units each having one or more Vgrooves 710. Such units can be used to form various fiber devices.Hence, a batch fabrication process may be used to process the substrate110 and to simultaneously form multiple fiber devices with V grooves710.

A single fiber can be threaded through different V grooves 710 in acolumn 730 between the surfaces 112 and 114 via the openings 131 and132. FIG. 7B shows an example where the fiber 140 is threaded through Vgrooves 710A, 710B, 710C, and 710D formed along a straight line on thesurface 112 of the substrate 110. A spacer 721, such as a rod, may beoptionally positioned on the surface 114 between the openings of twoadjacent V grooves to provide a support to the fiber 140. Such supportmay be used to reduce sharp bending of the fiber 140 which may damagethe fiber 140. After bonding and polishing the fiber 140, a couplingport is formed at each V groove on the surface 112 and is operable tocouple optical energy out of or into the fiber 140. Therefore, thisdevice has multiple coupling ports on the surface 112 to couple opticalenergy into or out of the fiber 140. When a proper control mechanism isimplemented at each coupling port, optical switching, opticalmultiplexing, and other coupling operations may be achieved.

FIGS. 7C and 7D show additional embodiments of fiber devices that twodifferent grooves 750 and 760 on the substrate 110 are not aligned alonga straight line as in FIGS. 7A and 7B but form an angle with respect toeach other. Numerals 751, 752, 761, and 762 indicate the openings of thegrooves 750 and 760 that penetrate through the substrate 110. In FIG.7C, the two grooves 750 and 760 are spaced from each other. A fiber maybe placed in the grooves 750 and 760 by sequentially passing the fiberthrough the openings 761, 762, 752, and 751. In FIG. 7D, two grooves 750and 760 are share a common opening 752. Such arrangements may becombined with aligned grooves.

Referring back to FIG. 1, the groove 120 with its two openings 131 and132 may be formed on both sides 112 and 114 of the substrate 110 in thefollowing manner. First, two adjacent grooves respectively formed indifferent sides of the substrate are aligned along the same groovedirection. Second, the groove on one side shares an opening with theadjacent groove on the opposite side of the substrate 110. Techniquessuch as the double-sided photolithography may be used to form the Vgrooves on both surfaces of the substrate. Unlike the fiber device shownin FIG. 7B where the coupling ports are only on a single side of thesubstrate, a substrate with V grooves on both sides can form a fiberdevice with coupling ports on both sides of the substrate. Suchdouble-sided coupling capability can provide flexible and versatilecoupling configurations in various fiber devices.

FIGS. 8A, 8B, and 8C illustrate one example of a fiber device 800 thathas V grooves on both sides 112 and 114 of the substrate 110. A first Vgroove 820 is formed on the side 114. Similar to the V grooves in FIGS.5B and 6, the depth and width of the V groove 820 increase from itscenter towards both ends 820A and 820B. A second, similar V groove 810is formed on the opposite side 112 along the same groove direction. Theend 810A of the second groove 810 overlaps with the end 820A of thefirst V groove 820 to create a through hole 812 that connects the Vgrooves 810 and 820. A third V groove 830 is also shown on the side 112to have one end 830A overlap with the end 820B of the V groove 820 onthe opposite side 114. A through hole 822 is then formed at theoverlapping region to connect the V groove 820 to the V groove 830. Afiber 140 is shown in FIG. 8C to thread through the holes 812 and 822 toform coupling ports on both sides 112 and 114 of the substrate 110.

FIG. 8D shows a 3-port fiber device 840 that is formed by dicing alinear array of V grooves 810, 820, and 830 from the substrate 110.Comparing to the single-side device shown in FIG. 7B, the naturalcurvature of the V grooves formed on both sides eliminates the spacers740. Similar to the batch fabrication of the single-sided devices shownin FIG. 7A, multiple double-sided devices may also be simultaneouslyfabricated from a single substrate as illustrated in FIG. 9.

In the above devices with V grooves formed on both sides of thesubstrate, two adjacent V grooves, located on opposite sides of thesubstrate, may not be aligned along a straight line but form an anglewith each other as illustrated by the adjacent grooves formed on thesame side shown in FIGS. 7C and 7D. Similar to the grooves in FIGS. 7Aand 7B, two adjacent V grooves, located on opposite sides of thesubstrate, may also be designed to spatially separate from each otherwithout sharing a common opening that penetrates through the substrateand extends between two sides of the substrate.

The openings in the above examples of V grooves are formed byanistropically etching for forming the V grooves. Hence, there is noneed to use a separate process to fabricate the openings if the etchingmask is properly designed. However, a separate fabrication step may alsobe used to form an opening and to achieve any desired geometric shape ofthe opening that may be difficult or impossible to make through etchingthe V grooves.

FIG. 10 illustrates a fiber device 1000 with aligned V grooves 810, 820,and 830 on both sides 112 and 114 of the substrate 110 that are spacedfrom one another by rectangular openings 1010 and 1020. V grooves 810and 830 are formed on the side 114 and the groove 820 is formed on theopposite surface 112 but is located between the grooves 810 and 830. Anetching process separate from etching of the V grooves is needed to formsuch openings 1010 and 1020. Other processing techniques such as lasermachining may also be used to form the openings.

The above fiber devices with V grooves either on one side or two sidesmay be used to form various fiber devices. Some exemplary devices aredescribed below.

FIG. 11 shows an optical fiber coupler 1100 by using two substrates 1110and 1120 each with V grooves on a single surface of the substrate. Thesubstrate 1110 has a surface 1110A on which three V grooves arefabricated and a fiber 140A is placed therein to form three couplingports 1111, 1112, and 1113. Similarly, the substrate 1120 has a surface1120A on which three V grooves are fabricated and a fiber 140B is placedtherein to form three coupling ports 1121, 1122, and 1123. The twosubstrates 1110 and 1120 are engaged by having the surfaces 1110A and1120A to face each other. The ports on one substrate substantiallyoverlap with the coupling ports of another substrate to allow energyexchange between the fibers 140A and 140B. Various techniques may beused to engage the two substrates together, such as optical epoxy, glassfrit thermal bond, CO2 laser assisted thermal bond.

A fiber device with V grooves on both sides of the substrate can be usedto provide coupling on both sides. More coupling flexibility can beachieved in such a device than a device with grooves on only one side.For example, each fiber in the device 1100 shown in FIG. 11 cannot beaccessed from the exposed surfaces 1110B and 1120B. Such access would bepossible if one of the two substrates 1110 and 1120 were designed tohave grooves on both sides. Thus, three or more substrates may bevertically stacked together to form a multi-layer optical coupler. Sinceeach substrate may have two or more fibers, coupling among many fibersin different substrates may be achieved.

FIG. 12 shows a 4-layer optical multi-port coupler 1200 having 4different double-sided substrates 1201, 1202, 1203, and 1204 based onthe designs shown in FIGS. 8D or 10. Four different fibers 1210, 1220,1230, and 1240 are respectively threaded in the substrates 1201, 1202,1203, and 1204. Two adjacent substrates, such as 1201 and 1202, may becoupled to form the coupling ports 1212, 1214, and 1216. Hence, opticalenergy can be coupled between any two fibers. For example, an opticalsignal in the fiber 1210 may be coupled to the fiber 1230 by firstcoupling into the fiber 1220 and then coupling from the fiber 1220 intothe fiber 1230. In general, a double-sided substrate can interface atboth sides with other single-sided or double-sided substrates.

FIG. 13A illustrates that optical coupling between two fibers indifferent layers may be controlled in a number of ways by controllingthe relative position of the two fibers in grooves. For example, nooptical coupling occurs between fibers 1301 and 1302 in the layers 1201and 1202 when they are placed in deep grooves to have a separation muchgreater than one wavelength of the light. The fibers 1303 and 1304 inthe layers 1202 and 1203 are positioned in shallow grooves so that aportion of each fiber's cladding is removed to allow for opticalcoupling. The depth of the grooves for the fibers 1303 and 1304 can becontrolled to control the coupling strength via evanescent fields. Thefibers 1305 and 1306, also in shallow grooves, are spatially offset inthe lateral direction so that the optical coupling is reduced with theamount of the offset.

The grooves for holding fibers 1301 and 1302 are “deep” grooves in thatthe depth of the groove is greater than the diameter of the fiber sothat the fiber cladding in the fiber portion in such grooves is notexposed above the substrate surface and no optical coupling port isformed. The grooves for holding the fibers 1303, 1304, 1305, and 1306,on the other hand, are “shallow” grooves as the groove 120 describedwith reference to FIG. 1 where a portion of a part of the fiber claddingprotrudes above the substrate surface when the fiber is placed in such agroove and can be removed to form an optical coupling port 144. Suchdeep and shallow grooves may be combined to provide flexibility andversatility in routing fibers and arranging optical coupling ports in afiber device.

FIG. 13B shows a single-sided substrate similar to the substrate in FIG.7B but processed to have both deep grooves 1312 and shallow grooves1310. Each deep grove 1312 is used at a location where optical couplingis undesirable. FIG. 13C shows a double-sided substrate with deepgrooves 1330 and shallow grooves 1320.

FIG. 14 further shows that a lateral jump-channel groove 1424 on asubstrate 1400 may be used to change the lateral direction of a fiber.The substrate 1400 is shown to have grooves on both sides. Solidelongated boxes such as 1410 represent grooves formed on one side andthe dashed elongated boxes such as 1412 represent grooves formed on theother side. The grooves 1410, 1412, 1414, 1416, and 1418 are alignedwith one another along a straight line to hold a fiber 1401. The groove1424 is a lateral jump-channel groove that is oriented with an anglerelative to adjacent grooves 1422 and 1436. Hence, a fiber 1402 can bethreaded through the lateral jump-channel groove 1424 to run throughgrooves 1440 and 1422 and then to change its direction to run throughgrooves 1436 and 1438. Lateral jump-channel grooves 1432 and 1444 arealso shown to direct the fiber 1402 from the groove 1430 to grooves 1456and 1458. A single-side substrate with grooves on one side may also bedesigned to have such lateral jump-channel grooves.

Such a lateral jump-channel can be combined with the verticalintegration of different double-side substrates to change the directionof an optical signal both laterally within a substrate and verticallyfrom one substrate to another substrate. This opens up possibilitysimilar to multi-layer printed circuit board technology allowingsophisticated connections from point to point and from layer to layer.

In the above devices, at least one buffer layer of a suitable materialsuch as a dielectric material like silicon dioxide or silicon nitridemay be formed over a groove under the fiber. This buffer layer may bedesigned to have certain mechanical or-thermal properties to stabilizethe structure formed by the substrate, the buffer layer, and the fiberby reducing the mechanical or thermal stress between the siliconsubstrate and the glass fiber. Therefore the reliability of the devicecan be improved. For example, if the substrate is formed of silicon, adielectric material with a coefficient of thermal expansion (CTE)between the CTE values of the silicon and the glass fiber may be used asthe buffer.

Although a few embodiments are described, various modifications andenhancements may be made without departing from the following claims.

What is claimed is:
 1. A device, comprising: a substrate having firstand second opposing substrate surfaces to form a first elongated grooveformed over said first substrate surface and first and second openingsrespectively formed at two ends of said first elongated groove, eachopening formed through said substrate to extend between said first andsecond substrate surfaces; and an optical fiber, which comprises a fibercore and a fiber cladding surrounding said fiber core, passing throughsaid first and second openings and having at least first, second, andthird contiguous fiber portions, wherein said second fiber portion isdisposed in said first elongated groove on said first substrate surface,and said first and said third fiber portions located on or over saidsecond substrate surface.
 2. The device as in claim 1, wherein saidsecond fiber portion includes an area where at least part of said fibercladding is removed to form an optical coupling surface whichevanescently couples optical energy into or out of said fiber core ofsaid optical fiber.
 3. The device as in claim 1, wherein said secondfiber portion is bonded to said first elongated groove.
 4. The device asin claim 1, wherein said first elongated groove has a V-shaped crosssection.
 5. The device as in claim 1, wherein said first elongatedgroove has a U-shaped cross section.
 6. The device as in claim 1,wherein said first elongated groove has a rectangular cross section. 7.The device as in claim 1, wherein said first elongated groove has across section forms at least a part of a circle.
 8. The device as inclaim 1, wherein said first elongated groove has a depth that increasesfrom a center between said first and said second openings towards saidfirst and said second openings.
 9. The device as in claim 1, whereinsaid first elongated groove has a width that increases from a centerbetween said first and said second openings towards said first and saidsecond openings.
 10. The device as in claim 1, further comprising asecond elongated groove formed on said second substrate surface andpositioned to have one end overlapping one of said first and said secondopenings to receive said third fiber portion, wherein said substratefurther includes another opening at another end of said second elongatedgroove to pass a fourth fiber portion adjacent to said third fiberportion through said substrate to be on or over said first substratesurface.
 11. The device as in claim 10, wherein said second elongatedgroove is oriented along an elongated direction of said first elongatedgroove.
 12. The device as in claim 10, wherein said second elongatedgroove is oriented to form a non-zero angle with respect to an elongateddirection of said first elongated groove.
 13. The device as in claim 10,wherein said third fiber portion includes an area where at least part offiber cladding is removed to form an optical coupling surface whichevanescently couples optical energy into or out of a core of saidoptical fiber.
 14. The device as in claim 10, wherein said secondelongated groove is sufficiently deep to keep said third fiber portionfrom protruding above said second substrate surface so that an opticalcoupling portion is not formed in said second fiber portion.
 15. Thedevice as in claim 10, further comprising a third elongated grooveformed on said first substrate surface and positioned to have one endoverlap said another opening of said second elongated groove to receivesaid fourth fiber portion.
 16. The device as in claim 15, wherein eachof said second, said third, and said fourth fiber portions includes anarea where at least part of fiber cladding is removed to form an opticalcoupling surface which evanescently couples optical energy into or outof a core of said optical fiber.
 17. The device as in claim 16, whereinat least two of said first, said second and said third grooves havedifferent groove depths.
 18. The device as in claim 16, furthercomprising a fourth opening at the other end of said third elongatedgroove to pass a fifth fiber portion adjacent to said fourth fiberportion through said substrate to be on or over said second substratesurface.
 19. The device as in claim 1, wherein said substrate furtherincludes: a second elongated groove formed on said second substratesurface and spaced from said first elongated groove along saidsubstrate; and first and second openings respectively formed at two endsof said second elongated groove, each opening formed through saidsubstrate to extend between said first and second substrate surfaces,wherein a portion of said fiber is disposed in said second groove. 20.The device as in claim 19, wherein said substrate if formed of siliconand said buffer layer is formed of silicon nitride or silicon dioxide.21. The device as in claim 1, further comprising a buffer layer formedbetween said groove and said fiber operable to reduce a mechanical orthermal stress between said fiber and said substrate.
 22. The device asin claim 1, wherein said substrate further includes: a second elongatedgroove formed on said first substrate surface and spaced from said firstelongated groove; and first and second openings respectively formed attwo ends of said second elongated groove, each opening formed throughsaid substrate to extend between said first and second substratesurface.
 23. The device as in claim 22, wherein one opening at one endof said second elongated groove receives a fourth fiber portion adjacentto said third fiber portion on said first substrate surface, whereinanother opening at another end of said second elongated groove receivesand passes a fifth fiber portion adjacent to said fourth fiber portionthrough said substrate to be on or over said second substrate surface,and wherein said fourth fiber portion is placed in said second elongatedgroove.
 24. The device as in claim 22, wherein said second elongatedgroove is oriented along an elongated direction of said first elongatedgroove.
 25. The device as in claim 22, wherein said second elongatedgroove is oriented to form an angle with an elongated direction of saidfirst elongated groove.
 26. The device as in claim 22, furthercomprising a spacer positioned on said second substrate surface betweensaid first and said second elongated grooves to support said third fiberportion and to reduce a bending of said third fiber portion.
 27. Thedevice as in claim 1, wherein said substrate is formed of asemiconductor, an insulator, or a metallic material.
 28. A method,comprising: providing a substrate having first and second opposingsubstrate surfaces; processing said substrate to form an elongatedgroove over said first substrate surface; forming two openingsrespectively at two ends of said elongated groove and through saidsubstrate to extend between said first and second substrate surfaces;and threading an optical fiber through said two openings to place aportion of said fiber in said elongated groove on said first substratesurface and to place two adjacent portions of said fiber on two ends ofsaid portion on said second substrate surface.
 29. The method as inclaim 28, wherein said substrate is formed of a semiconductor material,wherein said processing includes an anistropic etching process to form aV-shaped cross section in said elongated groove.
 30. The method as inclaim 28, wherein a single fabrication process is used to form saidelongated groove and said two openings.
 31. The method as in claim 28,further comprising forming another elongated groove over said secondsubstrate surface, wherein one end of said another elongated grooveoverlaps with one of said two openings.
 32. The method as in claim 28,further comprising reducing a mechanical or thermal stress between saidoptical fiber and said substrate by forming a buffer layer in saidelongated groove between said substrate and said optical fiber.
 33. Adevice, comprising: first and second substrates, each substrate havingfirst and second opposing substrate surfaces to include an elongatedgroove formed over said first substrate surface and two openingsrespectively formed at two ends of said elongated groove that go throughsaid substrate to extend between said first and second substratesurfaces; a first optical fiber passing through said two openings insaid first substrate to have a fiber portion positioned in saidelongated groove in which a portion of fiber cladding is removed to forma first optical coupling port; and a second optical fiber passingthrough said two openings in said second substrate to have a fiberportion positioned in said elongated groove in which a portion of fibercladding is removed to form a second optical coupling port, wherein saidfirst substrate surfaces of said first and said second substrates arepositioned to face each other to allow evanescent coupling between saidfirst and said second optical fibers through said first and secondoptical coupling ports.
 34. The device as in claim 33, wherein at leastone of said first and said second substrates includes a semiconductormaterial, an insulator material, or a metallic material.
 35. The deviceas in claim 33, wherein said first and said second optical couplingports are spatially shifted along a direction parallel to each substrateto control a strength of said evanescent coupling.
 36. The device as inclaim 33, wherein depths of said elongated grooves in said first andsaid second substrates are selected to control an evanescent couplingstrength between said first and said second optical coupling ports. 37.The device as in claim 33, wherein each substrate includes at leastanother elongated groove on said first substrate surface and twoopenings respectively formed at two ends of said another elongatedgroove that go through said substrate to extend between said first andsaid second substrate surfaces, wherein said another elongated groove insaid first substrate receives another portion of said first fiber toform a third optical coupling port by removing part of fiber cladding,and wherein said another elongated groove in said second substratereceives another portion of said second fiber to form a fourth opticalcoupling port by removing part of fiber cladding, and said third andsaid fourth optical coupling ports are positioned to provide evanescentcoupling between said first and said second fibers.
 38. The device as inclaim 33, wherein said second substrate includes a second elongatedgroove formed over said second substrate surface and positioned to haveone end overlap one of said two openings of said elongated groove onsaid first substrate surface to receive said fiber, wherein saidsubstrate further includes another opening at another end of said secondelongated groove to pass said fiber from said second substrate surfaceto said first substrate surface, and the fiber cladding of a portion ofsaid fiber in said second elongated groove is removed to form a thirdoptical coupling port, and said device further comprising: a thirdsubstrate having first and second opposing substrate surfaces to includean elongated groove formed over said first substrate surface and twoopenings respectively formed at two ends of said elongated groove thatgo through said third substrate to extend between said first and secondsubstrate surfaces; a third optical fiber passing through said twoopenings in said third substrate to have a fiber portion positioned insaid elongated groove in which a portion of fiber cladding is removed toform a fourth optical coupling port, wherein said first substratesurface of said third substrate is positioned to face said secondsubstrate surface of said second substrate to allow evanescent couplingbetween said second and said third optical fibers through said third andsaid fourth optical coupling ports.
 39. A device, comprising: asubstrate having first and second opposing substrate surfaces and first,second, and third openings that are spaced from one another and gothrough said substrate to extend between said first and said secondsubstrate surfaces; a first groove formed over said first substratesurface between said first and second openings to have a first endconnected to said first opening and a second end connected to saidsecond opening; a second groove formed over said second substratesurface between said second and third openings to have a first endconnected to said second opening and a second end connected to saidthird opening; and an optical fiber engaged to said substrate by passingthrough said first, second, and third openings in said substrate to havea first fiber portion positioned in said first groove and a second fiberportion positioned in said second groove.
 40. The device as in claim 39,wherein one of said first and said second fiber portions includes anarea where at least part of fiber cladding is removed to form an opticalcoupling surface.
 41. The device as in claim 39, wherein both said firstand said second fiber portions include an area where at least part offiber cladding is removed to form an optical coupling surface to allowoptical coupling with said optical fiber from both said first and saidsecond substrate surfaces.
 42. The device as in claim 39, furthercomprising a buffer layer formed between each substrate surface and saidoptical fiber operable to reduce a mechanical or thermal stress betweensaid optical fiber and said substrate.
 43. A device, comprising: asubstrate having first and second opposing substrate surfaces; a firstelongated groove formed over said first substrate surface; and first andsecond openings respectively formed at two ends of said first elongatedgroove, each opening formed through said substrate to extend betweensaid first and second substrate surfaces, wherein said first elongatedgroove has a depth that increases from a center between said first andsaid second openings towards said first and said second openings. 44.The device as in claim 43, wherein said first elongated groove has awidth that increases from a center between said first and said secondopenings towards said first and said second openings.
 45. The device asin claim 43, further comprising a second elongated groove formed on saidsecond substrate surface and positioned to have one end overlap one ofsaid two openings, wherein said substrate further includes anotheropening at another end of said second elongated groove.
 46. The deviceas in claim 45, wherein said second elongated groove is oriented alongan elongated direction of said first elongated groove.
 47. The device asin claim 45, wherein said second elongated groove is oriented to form anangle with an elongated direction of said first elongated groove. 48.The device as in claim 45, wherein said first and said second elongatedgrooves have different groove depths.
 49. The device as in claim 43,further comprising a fiber having a first portion positioned in saidfirst elongated groove over said first substrate surface, a secondportion immediately adjacent to said first portion to have a part insaid first opening and another part over said second substrate surface,and a third portion, which is also immediately adjacent to said firstportion, to have a part in said second opening and another part oversaid second substrate surface.